Galanthamine derivative, a process for its preparation and its use as a medicament

Abstract: This application relates to compounds of the formula wherein R¹, R² and R³ are defined within, which compounds are useful for the treatment of memory dysfunction characterized by decreased cholinergic function, pharmaceutical compositions containing the compounds and methods for making and using the compounds.

Description: The present invention relates to a galanthamine derivative, a process for its preparation and its use as a medicament. WO-A-88 08708 discloses galanthamine derivatives, including 6-O-demethyl-6-O-(dimethylaminocarbonyl) galanthamine, for the inhibition of acetylcholinesterase and useful in the treatment of Alzheimer's disease. This application provides a compound of the formula or a pharmaceutically acceptable addition salt thereof; which is useful for inhibiting acetylcholinesterase and alleviating various memory dysfunctions characterized by decreased cholinergic function such as Alzheimer's disease. This invention also provides a pharmaceutical composition useful for inhibiting acetylcholinesterase and alleviating various memory dysfunctions characterized by decreased cholinergic function which comprises a compound of the invention in an amount sufficient to affect cholinergic function and a pharmaceutically acceptable carrier. Unless otherwise stated or indicated, the following definitions shall apply throughout the specification and appended claims. The term "alkyl" shall mean a straight or branched alkyl group of the stated number of carbon atoms. Examples include methyl, ethyl, n-propyl, iso-propyl, n-butyl, isobutyl, sec-butyl, t-butyl, and straight and branched chain pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl and pentadecyl. The compound of the invention is prepared from the appropriate derivative of galanthamine as described more fully below and shown in Scheme I. The intermediate 6-demethylgalanthamine of Formula IV, a known compound, was prepared in a novel process by treating the galanthamine of Formula III with an alkaline salt of ethanthiol such as, for example, with EtSLi, EtSNa or EtSK. The reaction is typically carried out in a polar nonprotic solvent such as dimethylformamide (DMF) or N-methylpyrrolidone or a protic solvent such as butanol or pentanol at from about 80°C to about 135°C, preferably from about 90°C to about 125°C. The compound of Formula V wherein R 4 is hydrogen and R 5 is (C 1 -C 12 )alkyl is prepared by treating the compound of Formula IV with the appropriate isocyanato compound R 5 NCO. The reaction is carried out in an aprotic solvent such as, for example, tetrahydrofuran in the presence of base such as, for example, potassium carbonate at from about -10°C to about 30°C for from about 0.5 hours to about 4 hours. The compound of Formula I of the present invention can be used for the treatment of various memory dysfunctions characterized by decreased cholinergic function, such as Alzheimer's disease. The compound of the present invention is advantageous because it is less toxic and/or more potent than the related compounds known in the art. This utility is manifested by the ability of the present compound to inhibit the enzyme acetylcholinesterase and thereby increase acetylcholine levels in the brain. The ability to inhibit acetylcholinesterase was determined by the photometric method of Ellman et al., Biochem. Pharmacol. 7,88 (1961). This utility can also be ascertained by determining the ability of these compounds to restore cholinergically deficient memory in the Dark Avoidance Assay. In this assay mice are tested for their ability to remember an unpleasant stimulus for a period of 24 hours. A mouse is placed in a chamber that contains a dark compartment; a strong incandescent light drives it to the dark compartment, where an electric shock is administered through metal plates on the floor. The animal is removed from the testing apparatus and tested again, 24 hours later, for the ability to remember the electric shock. If scopolamine, an anticholinergic that is known to cause memory impairment, is administered before an animal's initial exposure to the test chamber, the animal reenters the dark compartment shortly after being placed in the test chamber 24 hours later. This effect of scopolamine is blocked by an active test compounds, resulting in a greater interval before re-entry into the dark compartment. An effective quantity of the compounds of the invention may be administered to a patient by any of the various methods, for example, orally as in capsule or tablets, parenterally in the form of sterile solutions or suspensions, and in some cases intravenously in the form of sterile solutions. The free base final products, while effective themselves, may be formulated and administered in the form of their pharmaceutically acceptable acid addition salts for purposes of stability, convenience of crystallization, increased solubility and the like. Acids useful for preparing the pharmaceutically acceptable acid addition salts of the invention include inorganic acids such as hydrochloric, hydrobromic, sulfuric, nitric, phosphoric and perchloric acids, as well as organic acids such as tartaric, citric, acetic, succinic, maleic, fumaric and oxalic acids. The active compound of the present invention may be orally administered, for example, with an inert diluent or with an edible carrier, or they may be enclosed in gelatin capsules, or they may be compressed into tablets. For the purpose of oral therapeutic administration, the active compound of the invention may be incorporated with excipients and used in the form of tablets, troches, capsules, elixirs, suspensions, syrups, wafers, chewing gum and the like. These preparations should contain at least 0.5% of active compounds, but may be varied depending upon the particular form and may conveniently be between 5% to about 70% of the weight of the unit. The amount of active compound in such compositions is such that a suitable dosage will be obtained. Preferred compositions and preparations according to the present invention are prepared so that an oral dosage unit form contains between 1.0 - 200 milligrams of active compound. The tablets, pills, capsules, troches and the like may also contain the following ingredients: a binder such as micro-crystalline cellulose, gum tragacanth or gelatin: an excipient such as starch or lactose, a disintegrating agent such as alginic acid, Primogel, cornstarch and the like; a lubricant such as magnesium stearate or Sterotex; a glidant such as colloidal silicon dioxide; and a sweeting agent such as sucrose or saccharin may be added or a flavoring agent such as peppermint, methyl salicylate, or orange flavoring. When the dosage unit form is a capsule, it may contain, in addition to materials of the above-type, a liquid carrier such as a fatty oil. Other dosage unit forms may contain other various materials which modify the physical form of the dosage unit, for example, as coatings. Thus, tablets or pills may be coated with sugar, shellac, or other enteric coating agents. A syrup may contain, in addition to the active compound, sucrose as a sweetening agent and certain preservatives, dyes, colorings and flavors. Materials used in preparing these various compositions should be pharmaceutically pure and non-toxic in the amounts used. For the purpose of parenteral therapeutic administration, the active compounds of the invention may be incorporated into a solution or suspension. These preparations should contain at least 0.1% of active compound, but may be varied between 0.5 and about 30% of the weight thereof. The amount of active compound in such compositions is such that a suitable dosage will be obtained. Preferred compositions and preparations according to the present invention are prepared so that a parenteral dosage unit contains between 0.5 to 100 milligrams of active compound. The solutions or suspensions may also include the following components: a sterile diluent such as water for injection, saline solution, fixed oils, polyethylene glycols, glycerine, propylene glycol or other synthetic solvents; antibacterial agents, such as benzyl alcohol or methyl parabens; antioxidants such as ascorbic acid or sodium bisulfite; chelating agents such as ethylenediaminetetraacetic acid; buffers such as acetates; citrates or phosphates and agents for the adjustment of tonicity such as sodium chloride or dextrose. The parenteral multiple dose vials may be of glass or plastic. The following examples will further illustrate this invention. REFERENCE EXAMPLE 1 6-O-Demethylgalanthamine To a stirred solution of 20 ml of dry DMF at -40°C under nitrogen was added 0.57 ml (0.48 g) of ethanethiol. The mixture was stirred for several minutes at -40 □ to -30°C after which 2.84 ml of 2.5 M BuLi in hexanes was added slowly by syringe at -40° to -50°C. The solution was then allowed to warm to room temperature over 15 minutes, heated to 50° under aspirator vacuum and again cooled to 30°C. To the solution was added a solution of 0.57 g of galanthamine in 5.7 ml of dry DMF. The solution was stirred at 95-100°C for 2 hours and subsequently at 100-105°C for 3 hours, allowed to cool to room temperature and concentrated to an oil. The oil was dissolved in chloroform, shaken with NH 4 Cl, made basic with aq NaHCO 3 and extracted four times with CHCl 3 . The pH of the aqueous layer was then adjusted to 9-10 with NH 4 OH and again extracted four times with chloroform. The combined organic extracts were dried (Na 2 SO 4 ), filtered and concentrated to an oil. The oil was dissolved in degassed 5% methanol/chloroform and flash chromatographed on silica gel eluting with the same solvent system followed by 10% methanol/chloroform to provide a beige solid. The material was dissolved in acetone and allowed to crystallize overnight to provide 0.298 g of 6-O-demethylgalanthamine, m.p. 225-229°C . ANALYSIS : Calculated for C 16 H 19 NO 3 70.31%C 7.01%H 5.12%N Found 70.14%C 7.29%H 4.96%N EXAMPLE 2 6-O-Demethyl-6-O-(n-heptylaminocarbonyl)galanthamine hydrochloride To 0.614 g of 6-O-demethylgalanthamine and 0.62 g of milled potassium carbonate was added by syringe 10.5 ml of dry THF. The suspension was cooled in an ice/salt bath after which 0.4 ml of n-heptylisocyanate was added by syringe. The mixture was stirred for 20 minutes at ice bath temperature, allowed to warm to room temperature and stirred at room temperature for 15 minutes. The solution was diluted with dry dichloromethane, cooled in an ice bath to room temperature and poured onto a silica gel column packed with 3% dry methanol/dichloromethane. The column was eluted with this solvent system followed by 5% dry methanol/dichloromethane to provide 0.852 g of an oil. The material was dissolved in ether and the hydrochloride salt precipitated by addition of ethereal hydrogen chloride, filtered and dried to provide 0.711 g of white crystals. Recrystallization/trituration from isopropyl alcohol provided 0.536 g of 6-O-demethyl-6-O-(n-heptylaminocarbonyl)galanthamine hydrochloride, m.p. 222-224°C. ANALYSIS : Calculated for C 24 H 34 N 2 O 4 • HCl 63.92%C 7.82%H 6.21%N Found 63.88%C 8.19%H 6.06%N

Claims: 6-O-demethyl-6-O-(n-heptylaminocarbonyl)galanthamine or a pharmaceutically acceptable acid addition salt thereof. A pharmaceutical composition which comprises the compound claimed in claim 1 and a pharmaceutically acceptable carrier therefor. Use of the compound as claimed in claim 1 for the preparation of a medicament being useful for the treatment of memory dysfunction characterised by decreased cholinergic function.

Inventors: DAVIS LARRY, KOSLEY RAYMOND W JR, TABERNA VERONICA, DAVIS, LARRY, KOSLEY, RAYMOND W., JR., TABERNA, VERONICA
Applicants: AVENTIS PHARMA INC, AVENTIS PHARMACEUTICALS INC.
Application year: 1994
Main classification: C07D491
IPC codes: C07D223, A61K31, C07D491, C07D307, A61P25